1. Field of the Invention
The present invention relates in general to a composition of matter for preparing substrates and more specifically to an improved solution and method for priming metallic sufaces and inner layers used in the manufacture of printed circuit boards (PCBs), chemically milled alloys, and chemically plated alloys.
2. Description of Related Art
PCB fabrication requires that substrate materials be processed. In general, substrate processing is chemically performed by sequentially coating a variety of chemical solutions onto the substrates. The substrates are commonly rinsed between application of each solution and then undergo a final rinsing and drying cycle. PCB processing can include steps in which layers of materials are cleaned, scrubbed, etched, passivated, treated, masked, processed, deposited or various combinations thereof.
An initial step in the PCB fabrication process involves the cleaning and priming of substrates for subsequent application of photoresists or screen inks used to define the desired PCB circuit pattern. FIG. 1 illustrates a typical four step technique used to chemically clean and prime substrate materials. This cleaning and priming technique is merely illustrative of one of many multi-step techniques typically used in the PCB fabrication industry.
During the first step, substrates are coated with an acidic solution which functions as a cleaner and chromate remover for approximately 30 seconds to 5 minutes. This solution is usually applied at a temperature of 100 to 120 degrees fahrenheit. The substrates are then rinsed to remove excess acidic solution.
During the second step, the substrates are surface etched by coating the substrates with an etching solution, commonly persulfate or peroxy-sulfuric. Alternatively, the substrates can be physically scrubbed with pumice. Etching removes remaining chromate and roughens the surface structure of the substrate. Etching also assists in adhesion of the resist to the substrate, especially if the substrate has an underlying copper component. The substrates are then rinsed to remove the etching solution or pumice particles.
The third step varies depending on if the substrate was chemically etched or pumice scrubbed. If chemically etched, the rinse step is followed by immersion in an second acidic solution. Commonly, a 5% to 10% sulfuric acid dip or spray is used to remove oxides which tend to form on etched copper and passivates the copper. Oxide removal slows re-oxidation of the substrates during the final rinse and drying cycle which occurs prior to lamination with resist. If pumice scrubbed, a medium to high pressure rinse is used to remove the pumice particles, which otherwise would typically not be removed.
The fourth step involves coating the substrates with an oxidation inhibitor and/or adhesion promoter for the resist. Triazole solutions are commonly used for this purpose. The substrates are then rinsed and dried. At this point, the substrates are primed and properly prepared for application of a resist layer.
However, multi-step cleaning and priming techniques are time-consuming, cost-prohibitive and create additional waste products. There is thus a need for a single-step method and formulation which cleans and primes PCB substrates and, more specifically, functions as a cleaner, chromate remover, oxidation inhibitor, adhesion promotor, flexibility enhancer and redeposition inhibitor.
The chemical milling industry uses processes similar to that described above to clean and prime substrates. There is thus a need for a single-step method and compound which primes substrates used in the manufacture of chemically milled alloys.
The chemical plating industry uses processes similar to that described above to clean and prime substrates. There is thus a need for a single-step method and compound which primes substrates used in the manufacture of chemically plated alloys.